This project concerns regulation of expression of genes encoding lens fiber membrane proteins involved in cell-cell communication. We are presently studying the regulation of expression of the gene encoding the major intrinsic protein (MIP) of the lens fiber membrane, which belongs to an ancient superfamily of putative transmembrane channel proteins. We cloned 2,840 bp of 5' flanking sequence of the human MIP gene to study the cis regulatory elements responsible for the tissue specificity and developmental regulation of the MIP gene. We found that a DNA fragment containing 253 bp of 5' flanking sequence and 42 bp of exon 1 of the human MIP gene fused to the reporter chloramphenicol acetyltransferase (CAT) gene is able to express the CAT gene in lens cells in transient assays and transgenic mice. We are presently studying the effect of several transcription factors on the in vitro transcription of the MIP gene in Drosophila and HeLa nuclear extracts. Purified human Sp1 activates the in vitro transcription of the MIP promoter, suggesting its involvement in the transcriptional regulation of the MIP gene. These studies will further our understanding of the role of general transcription factors on the tissue-specific expression of the MIP gene.